As the Spry(and any Ajax framework) files aren't the smallest set of files to add to your page you don't want the user to download them if they don't need to. The way I add the Spry files to a display template in Model Glue is per event via a variable defined in the XML controller. For this example I'm going to include the SpryCollapsiblePanel.js file.
If you're going to do it in the ModelGlue.xml, you could also do it as a separate include. <inc1ude name="javascript" template="spryincludes.cfm" /> You would then simply have a spot to plug in "javascript" in your template just like you have a spot for "body".